Persons operating projectors, especially optometrists and ophthalmologists find it is necessary to face the patient while the patient looks straight ahead, over the operator's shoulder, at a primary image caused by a projector. This is so that the operator can adjust the lenses of the patient until the patient is able to see the primary image clearly. Such work is rather difficult because, in the past, the operator would frequently have to turn around in order to check and see the correctness of the image as reported to him by the patient. This invention is of a device which is adapted to be attached to the projector and which taps a portion of the main projector beam and reflects it onto a surface in a convenient line of sight directly in front of the operator or to his right or left side, with the result that he does not have to continually turn his head to check to see if the patient has read the projected image correctly.
This device embodies a principle expressed by James P. C. Southall in his text "Mirrors, Prisms, and Lenses," to the effect that "if a ray lying in a principal section is reflected successively at two plane mirrors, it will be deviated from its original direction by an angle equal to twice the dihedral angle between the mirrors." The device further utilizes a principle disclosed in U.S. Pat. No. 3,768,891, wherein a duplicate image of a main projected image can be caused by positioning a mirror in the peripheral zone of the main beam and reflecting the same by that mirror and another mirror to cause a secondary image to appear, which is a duplicate of the original.
Accordingly, this invention has as an object the provision of an improvement comprising a device for use with an optical projector system to produce a duplicate image simultaneously with the main image caused by the projector and wherein the duplicate image is beamed in a direction which is 180 degrees from the path of the beam of light from the projector causing the main image or, alternatively, at an angle of 90 degrees with respect to that path and wherein the operator may, at his option, select the surface upon which the secondary or duplicate image will be beamed, all with the object of permitting an operator of a projector to face the projector, and the patient, for various adjustments of it while, at the same time, he is able to see a secondary or duplicate image in front of him or to his side which is the same as that which the patient sees and which device may be readily installed on existing projectors.
Generally speaking the optical device has as an object the provision of an improved system which may be incorporated in existing projector systems and which includes a tubular member or means, preferably with a lens system, and which includes opposite ends which are rotatable with respect to the longitudinal centerline of the tubular member and on each of which a mirror is mounted at a predetermined and selected angle so that light may enter through an opening in the tubular member and be reflected through it from a first mirror to the second mirror to be reflected upon a secondary surface causing a duplicate image.
In accordance with these general objects, this invention will now be described with reference to the accompanying drawings, in which: